Motor vehicles, such as, for example, hybrid vehicles and electric vehicles use propulsion systems to provide motive power. In hybrid vehicles, the propulsion system most commonly refers to gasoline-electric hybrid vehicles, which use gasoline (petrol) to power internal-combustion engines (ICEs), and electric batteries to power electric motors. These hybrid vehicles recharge their batteries by capturing kinetic energy via regenerative braking. When cruising or idling, some of the output of the combustion engine is fed to a generator (merely the electric motor(s) running in generator mode), which produces electricity to charge the batteries. This contrasts with all-electric cars which use batteries charged by an external source such as the grid, or a range extending trailer. Nearly all hybrid vehicles still require gasoline as their sole fuel source though diesel and other fuels such as ethanol or plant based oils have also seen occasional use.
Batteries and cells are important energy storage devices well known in the art. The batteries and cells typically comprise electrodes and an ion conducting electrolyte positioned therebetween. Battery packs that contain lithium ion batteries are increasingly popular with automotive applications and various commercial electronic devices because they are rechargeable and have no memory effect. Storing and operating the lithium ion battery at an optimal operating temperature is very important to allow the battery to maintain a charge for an extended period of time.
Due to the characteristics of the lithium ion batteries, the battery pack operates within an ambient temperature range of −20° C. to 60° C. However, even when operating within this temperature range, the battery pack may begin to lose its capacity or ability to charge or discharge should the ambient temperature fall below 0° C. Depending on the ambient temperature, the life cycle capacity or charge/discharge capability of the battery may be greatly reduced as the temperature strays from 0° C. Nonetheless, it may be unavoidable that the lithium ion battery be used where the ambient temperature falls outside the ambient temperature range.
Alluding to the above, in a battery or battery assembly with multiple cells, significant temperature variances can occur from one cell to the next, which is detrimental to performance of the battery pack. To promote long life of the entire battery pack, the cells must be below a desired threshold temperature. To promote pack performance, the differential temperature between the cells in the battery pack should be minimized. However, depending on the thermal path to ambient, different cells will reach different temperatures. Further, for the same reasons, different cells reach different temperatures during the charging process. Accordingly, if one cell is at an increased temperature with respect to the other cells, its charge or discharge efficiency will be different, and, therefore, it may charge or discharge faster than the other cells. This will lead to decline in the performance of the entire pack.
The art is replete with various designs of the battery packs with cooling systems. The U.S. Pat. No. 5,071,652 to Jones et al. teaches a metal oxide-hydrogen battery including an outer pressure vessel of circular configuration that contains a plurality of circular cell modules disposed in side-by-side relations. Adjacent cell modules are separated by circular heat transfer members that transfer heat from the cell modules to the outer vessel. Each heat transfer member includes a generally flat body or fin which is disposed between adjacent cell modules. A peripheral flange is located in contact with the inner surface of the pressure vessel. The width of each cell module is greater than the length of the flange so that the flange of each heat transfer member is out of contact with the adjacent heat transfer member. The flanges are constructed and arranged to exert an outward radial force against the pressure vessel. Tie bars serve to clamp the cell modules and heat transfer members together in the form of a stack which is inserted into the pressure vessel.
The metal oxide-hydrogen battery taught by the U.S. Pat. No. 5,071,652 to Jones et al. is designed for cylindrical type of batteries. The U.S. Pat. No. 5,071,652 to Jones et al. teaches the heat transfer members be in direct contact with the vessel. Thus the U.S. Pat. No. 5,071,652 to Jones et al. does not teach creating a clearance between the vessel and the heat transfer members, which can be used to introduce cooling or heating agent to cool or heat the cells.
The U.S. Pat. No. 5,354,630 to Earl et al. teaches a common pressure vessel of a circular configuration type Ni—H2 storage battery having an outer pressure vessel that contains a stack of compartments. Each of the compartments includes at least one battery cell, a heat transfer member, and a cell spacer for maintaining a relatively constant distance between adjacent compartments. The heat transfer members include a fin portion, which is in thermal contact with the battery cell, and a flange portion which extends longitudinally from the fin portion and is in tight thermal contact with the inner wall of the pressure vessel. The heat transfer member serves to transfer heat generated from a battery cell radially to the pressure vessel.
Similar to the metal oxide-hydrogen battery taught by the U.S. Pat. No. 5,071,652 to Jones et al., the storage battery taught by the U.S. Pat. No. 5,354,630 to Earl et al. is designed for cylindrical types of batteries. This metal oxide-hydrogen battery taught by the U.S. Pat. No. 5,354,630 to Earl et al. has the heat transfer members being in direct contact with the vessel thereby failing to create a clearance between the vessel and the heat transfer members which can be used to introduce cooling or heating agent to cool or heat the cells.
The U.S. Pat. No. 6,117,584 to Hoffman et al. teaches a thermal conductor for use with an electrochemical energy storage device. The thermal conductor is attached to one, or both, of the anode and cathode contacts of an electrochemical cell. A resilient portion of the conductor varies in height or position to maintain contact between the conductor and an adjacent wall structure of a containment vessel in response to relative movement between the conductor and the wall structure. The thermal conductor conducts current into and out of the electrochemical cell and conducts thermal energy between the electrochemical cell and thermally conductive and electrically resistive material disposed between the conductor and the wall structure. The thermal conductor taught by the U.S. Pat. No. 6,117,584 to Hoffman et al. is attached to one or both of the anode and cathode contacts of the cell and not between the cells.
The U.S. Pat. No. 6,709,783 to Ogata et al. teaches a battery pack having a plurality of prismatic flat battery modules constituted by nickel metal hydride batteries, arranged parallel to each other. Each battery module consists of an integral case formed by mutually integrally connecting a plurality of prismatic battery cases having short side faces and long side faces, the short side faces constituting partitions between adjacent battery cases and being shared. A plurality of spacers are made of a sheet bent in opposite directions such that alternately protruding grooves or ridges respectively contact the opposite long side faces of the battery modules for providing cooling passages between the battery modules. The battery pack taught by the U.S. Pat. No. 6,709,783 to Ogata et al. is intended to define voids, i.e. the cooling passages between the cells thereby diminishing the packaging characteristics of the pack.
The U.S. Pat. No. 6,821,671 to Hinton et al. teaches an apparatus for cooling battery cells. As shown in FIG. 1 of the U.S. Pat. No. 6,821,671 to Hinton et al., a cooling fin is connected to the battery cell having railings for holding the cooling fin as each cooling fin slides between the railings thereby fitting the cooling fin within the respective battery cell thereby forming the aforementioned apparatus. The engagement of the cooling fin with the battery cell is presented in such a manner that the cooling fins do not extend beyond the battery cells. Thus, the cooling agent only serves its intended purpose if introduced from the side of the apparatus. If, for example, the cooling agent is applied to the front of the apparatus, only first battery cell is exposed to the cooling agent thereby preventing effective cooling of other battery cells.
Alluding to the above, FIG. 7 of the U.S. Pat. No. 6,821,671 to Hinton et al. shows the apparatus wherein straps are inserted through ears extending from the cooling fins to connect multiple battery cells to form the apparatus and fins together to keep the battery cells in compression. The straps, as shown in FIG. 7 deform the battery cells thereby negatively affecting chemical reaction between electrolyte, cathodes and anodes of each battery cells and resulting in a reduced life span of the cells.
The Japanese publication No. JP2001-229897 teaches a battery pack design and method of forming the same. The purpose of the method is to create the voids between the cells for cool air to go through the voids and between the cells to cool the cells. Similar to the aforementioned U.S. Pat. No. 6,709,783 to Ogata et al., the battery pack taught by the Japanese publication No. JP2001-229897 is intended to define the voids between the cells thereby diminishing the packaging characteristics of the pack.
Packaging of lithium battery cells is one of the areas of continuous development and research. Generally, the lithium battery cells packaged in a metallic case are known, as shown, for example, in U.S. Pat. No. 6,406,815. These metallic cases have the advantage of protecting the cells from handling and vibration damage. They are also dimensionally consistent, allowing for combining of multiple cases into a single large pack as disclosed in U.S. Pat. No. 6,368,743. However, the metallic cases are expensive to manufacture and each different configuration requires new dies to produce the various components and new tools to assemble those components. Consequently, techniques and materials for enclosing lithium battery cells in envelopes creating lithium battery cell packs have been developed, one type of which is disclosed in U.S. Pat. No. 6,729,908. Unfortunately, these packages do not provide structural rigidity or protection from handling and vibration nearly as well as the metallic cases, nor can they be combined into consistently sized groups of cells because of the inherent variation in the thickness of a lithium battery cell pack.
Therefore, there remains an opportunity to improve upon the packs of lithium batteries of the prior art to increase the ambient temperature range at which the lithium battery operates and to provide a new battery pack with improved packaging and safety characteristics.
Also, there remains an opportunity to maintain the battery pack at the optimal operating temperature to ensure the longest possible life cycle, rated capacity, and nominal charge and discharge rates.
There is also an opportunity provide a new frame design that will present structural rigidity or protection from handling and vibration nearly as well as the metallic cases, as the cells are combined into consistently sized groups of cells or modules because of the inherent variation in the thickness of a lithium battery module or cell pack. Also there remains another opportunity to provide a solution that allows escape of gases away from the passenger compartment of the vehicle as pressure inside the battery pack exceeds the normal pressure thereby preventing escape of gases in to the compartment to eliminate potential risk and any unwanted hazardous events to driver and/or passengers. A battery assembly of the present disclosure is adaptable to be utilized in various configurations including and not limited to horizontally or vertically stacked battery cell packaging configurations used in an automotive vehicle. A plurality of battery modules are housed in a container, such as, for example, a dish or support tray which may include a cover. The container may be supported by a floor pan assembly or other part of the vehicle. The container presents a base and a plurality of side walls extending therefrom. At least one pressure release device is disposed in the base or walls for allowing fluid such as gas, to escape beyond the dish. The pressure release device may be, for example, a rupture element or disk formed by scoring or otherwise weakening areas of the container or a valve device. In one embodiment, a plurality Of rupture elements are disposed in the walls of the container. The rupture elements may present scoring lines that rupture under high pressure. As an alternative to the rupture elements, the battery assembly may include a valve device that would enable low pressure venting as well as emergency high pressure venting. In one embodiment, the valve device is disposed in the base of the container and is configured to selectively open and close an opening formed in the base of the container. In one embodiment, the valve device includes a closure plate with a seal or O-ring, a spring retainer portions of which extend across the opening in the base of the dish, a rod with a compression plate that is spaced opposite from the closure plate, and a spring or biasing element disposed between the closure plate and the compression plate and secured by the spring retainer. In one embodiment, the spring retainer is in the form of a cross and includes a core portion and, illustratively, at least four radial portions with each presenting a high pressure break feature. The valve device and rupture elements provide an over pressure relief system and act as “bursting elements”. The areas wherein the devices are disposed are designed to break open during an event which would cause the pressure within the battery pack to exceed specified limits.
In one embodiment of the disclosed battery module, a potting material, such as for example, polyurethane, polyurethane foams, silicones or epoxies, is injected into the battery module placed in a case to at least partially or fully encapsulate the battery module and the corresponding cells thereby eliminating air gaps between the module and the case. The potting material also serves to prevent the electrode stack from shifting inside the cell packaging material during exposure to shock and vibration. The potting material also prevents the cell packaging from relaxing over time and allowing the electrolyte to settle into the base of the cell package and thus reducing the cell's electrical capacity. The potting/encapsulating material also prevents movement of the battery module within the battery pack case. A wrap blanket is disposed between the module and the potting material thereby providing “green” solution to allow the user to remove the module from the dish and service the module or simply to recycle the pack in a highly efficient fashion.
An advantage of the present disclosure is to provide a solution that allows escape of gases away from the passenger compartment of the vehicle by placing pressure release elements in the dish, wherein the pressure release elements activate as pressure inside the pack exceeds the normal or predetermined pressure thereby preventing escape of gases in to the passenger compartment to eliminate potential risk and any unwanted hazardous events to driver and/or passengers.
Still another advantage of the present disclosure is to provide a battery module having excellent retention that surrounds and secures the cells.
Still another advantage of the present disclosure is to provide a battery module having excellent retention that surrounds and secures the electrode stack within the cell envelope from shifting.
Still another advantage of the present disclosure is to provide a battery module encapsulated by the potting material which greatly reduces the potential permeation of liquids into the battery pack, or leakage from inside the battery module to the outside of the battery pack thereby preventing reduced product life or premature failures of the battery module.
Still another advantage of the present disclosure is to provide a low mass design of a battery pack which includes polyurethane foam as a potential retention device, which is very competitive to that of traditional methods of retention, such as, for example, silicone or epoxy adhesives.
Still another advantage of the present disclosure is to provide a packaging method which utilizes a case that houses the module and an encapsulant which locks the module in position and will allow the pack to be mounted in any orientation.
Still another advantage of the present disclosure is to provide a battery pack that reduces manufacturing costs due to simplified assembly methods.
Still another advantage of the present disclosure is to provide a pack that is simple in design and has a reduced mass.
The disclosed battery assembly provides several advantages over the battery packs of the prior art by increasing an ambient temperature range at which the battery pack can operate. Also, the disclosed battery assembly helps maintain the battery pack at an optimal operating temperature to extend the life cycle of the battery pack, and to increase battery pack safety.